Cast iron manhole steps and ladder rungs have been known to the prior art and industry for decades. As early as 1936, in the patent art, one sees the "wall step" of Grove U.S. Pat. No. 2,064,803 issued Dec. 15, 1936 showing a steel core reinforced manhole step having rubber and cast iron coatings thereon. To the best of applicant's knowledge, the earliest forms of manhole steps were all "cast-in" or "fit-in" types in that, when the manhole itself (or segments thereof) were constructed or cast in the fabricator's yard, the manhole steps were then made or cast integral therewith. Insofar as a manhole or its equivalent would be constructed on site, the steps, ladder rungs or supports would be cast-in at the site or grouted in, in the case of masonry.
About 1969 or 1970 and in the several years following this date, steel core reinforced, plastic-coated, cast-in manhole steps of vaarious configurations were manufactured, offered for sale and sold by M.A. Industries, Inc., a Georgia Corporation of Peachtree City, Georgia. Apparently, at least ten different plastic coated, steel core reinforced manhole steps or types thereof were manufactured, on sale and sold before June 21, 1975 by this company.
On June 21, 1976, by application Ser. No. 698,490, entitled "Step Construction Employing Insertible Fastener Having Deformable Projections", there was filed in the USPTO a patent application directed to a drive-in or hammer-in manhole step construction, this application assigned, as an issued U.S. Pat. No. 4,100,997, issued July 18, 1978, to M.A. Industries, Inc., a Georgia Corporation, having a principal place of business at Kelly & Dividend Road, Peachtree City, Georgia 30269. This assignment is dated Aug. 9, 1983 and is recorded in the USPTO.
On information and belief, (1) at least by June 24, 1975 and very probably earlier, the invention of the Peacock U.S. Pat. No. 4,100,997 patent (but incorporating a steel core reinforcement) was on sale and, further, (2) at least by June 25, 1975 and very probably earlier, manhole steps incorporating the invention of the U.S. Pat. No. 4,100,997 Peacock patent (but incorporating a steel core reinforcement) had been sold, both the offer for sale and sale at least to Waukesha Cement Tile Co., Waukesha, Wisconsin as of the date given.